Television, 1947 style- 9
Another update is in order, I think.
Since finally getting my parcels out of the iron grip of MyHermes, I've been able to start making some progress on the power supply chassis. This is beginning to illustrate precisely why old TVs were so large and heavy- it already weighs a ton, due to the disproportionately large amount of vintage iron bolted on to it.
The above is a dry run, just blocking out roughly where everything will go. The large transformer on the right is the unit that came yesterday- I'm not sure what its original use was- it's been liberally painted grey and stamped 1944, so possibly has some kind of military origin. It's beautifully made, but not quite what I thought it was going to be. This isn't the vendor's fault, but probably my own- I noticed that two of the tappings were labelled '500', but didn't expect them to be labelled '500 c/s.' Lord knows what that is all about. It's got a primary with a third tap on it, one side being 180v and the other side being 230v, and I've discovered that I can feed 230v into the 180v primary without any obvious ill-effects, and get an HT voltage of 380v. It's not 500v, but it'll have to do- I'm reasonably confident that the set will work on the reduced HT without any problems. The transformer on the left that I mentioned in a previous post has been relegated to the job of smoothing choke- I shall simply run the HT through the secondary en route to the rest of the set, with a smoothing cap on either side to ground.
The two valves in the photo are duff- they normally live on my mantelpiece as ornaments, but they have similar dimensions to the U31 rectifiers I'm intending to fit. Up the back can be seen the larger HT smooting cap, and the EHT smoothing cap that will be fitted at a later stage. The large vacant space behind the power transformer will ultimately be occupied by the EHT cage, made from a pierced-steel in-tray that I rescued from a skip years ago, and containing the EHT rectifier valve, the EHT cap and the slightly idiosyncratic line output transformer that I'm going to have to wind myself. (It's actually more of a flyback transformer, as its only job will be to create EHT and the filament current for the rectifier valve, the line output matching and damping being carried out by the ferrite transformer on the combined sunch unit.) Or I might just cheat and use an old tripler unit instead.
This slightly thinner arrangement is the progress I've made so far- the two transformers are bolted down, and behind the choke the two sockets for the rectifiers are bolted in. I've also nicked a suitably period mains lead off a spare electric iron, and fitted an IEE socket for which, irritatingly, I made the hole slightly too large. Ah, well. The transformer-now-choke in the foreground I shall try out as it is first, but I fully expect it to saturate in use, so I may have to dismantle the core and re-arrange the laminations. In fact, I might even create a new winding for it that would better suit its new role as a smoothing choke, but I don't want to muck it up without good reason. It is a pretty crumbly bit of kit, though.
Here's the underside so far, although I stopped work when I realised I'd missed out a couple of additions that aren't in the original schematic, but would none the less be desirable. One is fuses, both in the mains supply and on the filament and HT rails- having hacked around sourcing all this old stuff, I don't really want to write any of it off with unexpected power surges or nasty shorts. The other is a connection for a remote switch- the PSU will live (hopefully) at the bottom of the cabinet, the on/off switch being of course mounted on the front of the console on a sort of umbilical lead, so I'll need to go back and splice that into the live somewhere.
And yes, there's yet another transformer under there. Fortunately, I deliberately made the chassis deep enough to conceal an extra transformer just in case, and having been compelled to jack up the output of the power transformer, all the lovely 6.3v heater tappings will now be delivering something like 10-12v, so I've had to fit another transformer solely to supply the heater voltage. Fortunately I've had this one knocking around for years. It's irritatingly wonky, which is odd, as it's bolted to two of the power transformer bolts, and that one is square to the chassis, so I'm not sure what happened there. In any case, it won't be seen.
The little square thing up above is the bridge rectifier. I was going to make a set of fins for this, but the chassis should provide more than adequate cooling, and as I've now included two rectifier valves as well (to control the inrush current) I thought I'd just discreetly hide it away and pretend I haven't succumbed to solid-state rectification..
Since finally getting my parcels out of the iron grip of MyHermes, I've been able to start making some progress on the power supply chassis. This is beginning to illustrate precisely why old TVs were so large and heavy- it already weighs a ton, due to the disproportionately large amount of vintage iron bolted on to it.
The above is a dry run, just blocking out roughly where everything will go. The large transformer on the right is the unit that came yesterday- I'm not sure what its original use was- it's been liberally painted grey and stamped 1944, so possibly has some kind of military origin. It's beautifully made, but not quite what I thought it was going to be. This isn't the vendor's fault, but probably my own- I noticed that two of the tappings were labelled '500', but didn't expect them to be labelled '500 c/s.' Lord knows what that is all about. It's got a primary with a third tap on it, one side being 180v and the other side being 230v, and I've discovered that I can feed 230v into the 180v primary without any obvious ill-effects, and get an HT voltage of 380v. It's not 500v, but it'll have to do- I'm reasonably confident that the set will work on the reduced HT without any problems. The transformer on the left that I mentioned in a previous post has been relegated to the job of smoothing choke- I shall simply run the HT through the secondary en route to the rest of the set, with a smoothing cap on either side to ground.
The two valves in the photo are duff- they normally live on my mantelpiece as ornaments, but they have similar dimensions to the U31 rectifiers I'm intending to fit. Up the back can be seen the larger HT smooting cap, and the EHT smoothing cap that will be fitted at a later stage. The large vacant space behind the power transformer will ultimately be occupied by the EHT cage, made from a pierced-steel in-tray that I rescued from a skip years ago, and containing the EHT rectifier valve, the EHT cap and the slightly idiosyncratic line output transformer that I'm going to have to wind myself. (It's actually more of a flyback transformer, as its only job will be to create EHT and the filament current for the rectifier valve, the line output matching and damping being carried out by the ferrite transformer on the combined sunch unit.) Or I might just cheat and use an old tripler unit instead.
This slightly thinner arrangement is the progress I've made so far- the two transformers are bolted down, and behind the choke the two sockets for the rectifiers are bolted in. I've also nicked a suitably period mains lead off a spare electric iron, and fitted an IEE socket for which, irritatingly, I made the hole slightly too large. Ah, well. The transformer-now-choke in the foreground I shall try out as it is first, but I fully expect it to saturate in use, so I may have to dismantle the core and re-arrange the laminations. In fact, I might even create a new winding for it that would better suit its new role as a smoothing choke, but I don't want to muck it up without good reason. It is a pretty crumbly bit of kit, though.
Here's the underside so far, although I stopped work when I realised I'd missed out a couple of additions that aren't in the original schematic, but would none the less be desirable. One is fuses, both in the mains supply and on the filament and HT rails- having hacked around sourcing all this old stuff, I don't really want to write any of it off with unexpected power surges or nasty shorts. The other is a connection for a remote switch- the PSU will live (hopefully) at the bottom of the cabinet, the on/off switch being of course mounted on the front of the console on a sort of umbilical lead, so I'll need to go back and splice that into the live somewhere.
And yes, there's yet another transformer under there. Fortunately, I deliberately made the chassis deep enough to conceal an extra transformer just in case, and having been compelled to jack up the output of the power transformer, all the lovely 6.3v heater tappings will now be delivering something like 10-12v, so I've had to fit another transformer solely to supply the heater voltage. Fortunately I've had this one knocking around for years. It's irritatingly wonky, which is odd, as it's bolted to two of the power transformer bolts, and that one is square to the chassis, so I'm not sure what happened there. In any case, it won't be seen.
The little square thing up above is the bridge rectifier. I was going to make a set of fins for this, but the chassis should provide more than adequate cooling, and as I've now included two rectifier valves as well (to control the inrush current) I thought I'd just discreetly hide it away and pretend I haven't succumbed to solid-state rectification..